In the signal reproducing apparatus such as the commonplace audio tape recorder or disk player, it is well-known that, when the reproducing speed, i.e. the speed at which audio signals recorded on a recording medium are reproduced, is changed with respect to the recording speed, i.e. the speed at which the audio signals are previously recorded on the recording medium, not only the reproducing speed or tempo but also the sound pitch or key is changed. That is, the higher the reproducing speed, the higher the sound pitch and, conversely, the slower the reproducing speed, the lower sound pitch.
In the apparatus for reproducing audio signal such as a performance of the background orchestra without the singer's voice, there are presented in the art various audio signal reproducing apparatus which is provided with such a reproducing function that the tempo or reproducing speed may be variably and arbitrarily set so that a performance of the background orchestra without the singer's voice may be reproduced at the tempo desired by the singer. In the signal reproducing apparatus provided with such variable speed reproducing function, the sound pitch or key is necessarily changed with changes in the reproducing speed. By this reason, a signal processing device provided with the function of changing the pitch or key of the reproduced audio signals is used for effecting a pitch conversion in such a manner that the pitch or key of the reproduced audio signals is not changed even though the reproducing speed is changed so that the reproduced audio signals may have approximately the same pitch as that used during the original recording.
The above mentioned signal processing apparatus are known in the art in which analog delay elements such as BBDs (bucket brigade devices) or CCDs (charge coupled devices) are used and the read or write clocks thereof are chronologically changed for controlling the delay time, or in which input audio signals are converted into digital signals and digital delay elements such as shift registers or RAMs (random access memories) are used for effecting time base compression and expansion through control of the writing and read-out operations.
The conventional type of the audio signal reproducing apparatus is constructed in the following manner. That is, with the tape recorder or the disk player, the running speed of the recording medium such as the magnetic tape or the disk (tape speed or rotating speed) is controlled by the reproducing speed control device so that the reproduced audio signals are reproduced from the variable speed reproducing apparatus and converted in pitch in the pitch conversion unit supplied at the signal output terminals. Information signals indicating changes in the reproducing speed are supplied from the reproducing speed control unit to the pitch conversion unit, which then performs a pitch conversion so that the sound pitch of the reproduced audio signal is lowered to 1/m times the standard sound pitch when the variable speed reproducing unit is operating at a speed m times the standard speed.
In the above described type of conventional audio signal reproducing apparatus for processing the pitch conversion of the reproduced audio signal, there is required an information indicating the ratio of the change caused in the reproducing speed. In addition, the variable speed reproducing unit and the variable speed control unit need to be controlled at all times under a predetermined relation to each other. Thus it is not feasible to variably independently control the tempo and the key of the reproduced audio signals.
In a reproduction of a performance of the background orchestra without the singer's voice many tunes are selectively reproduced, and the singers usually take their turns by rotation. With the audio signal reproducing apparatus used for reproducing a performance of the background orchestra without the singer's voice, the pitch conversion unit operates in the previous setting even when the tunes and/or the singers are changed, thus embarassing the singers.